Testing of packages

ABSTRACT

Packages (7) are conveyed through at least one, and preferably two, test stations (14, 16). At each station there is a test head (7) which is urged towards the conveying path, preferably by gravity. As a package (7) is conveyed through a station it displaces the head away from the path. The displacement is monitored. Preferably, subsequent displacement towards the path due to leakage of the package is also monitored.

The present invention relates to an apparatus and method for testingpackages, e.g. packages of snack foods such as bags of crisps.

It is known to test a package by applying a load which tends to compressthe package, and monitoring the effect. After an interval, the packagemay be tested again. For a good package, if the two tests use identicalloads, then the package should behave identically, e.g. in terms of theamount of compression. But if the package contains air or other fluidand has a leak, the first test will cause some deflation. Thus theamount of compression will be greater than for a good package.Furthermore the package will already be in a deflated state at the startof the second test, and will undergo further deflation (unless it isalready fully deflated). Testing equipment working on this principle hasbeen brought to quite a high level of sophistication, e.g. as describedin WO93/17317. But we have now found ways to improve the operation ofsuch test systems.

In a first aspect, the invention provides test apparatus having conveyormeans for conveying test substrates, and one or more test stationsarranged along the conveying path; there being at least one such teststation having a test head adapted to be moved towards and away from theconveying path; wherein the head is normally urged towards the conveyingpath so that a package being conveyed along the path contacts the headand urges it away from the conveying path; and wherein the resultingdisplacement of the head is monitored.

Desirably, the test head is urged solely by gravity towards theconveying path. Its contact surface is desirably such as to allowcontinuing movement of packages along the conveying surface. Itpreferably uses an array of low back line pressure rollers.

Since it is the arrival of a substrate that causes the movement of thetest head directly, there is no need for sophisticated devices forsynchronising the action of a test station with the arrival of apackage, or for synchronising the actions of a plurality of teststations. Since the arrival of a substrate acts to raise a test head, ifa second substrate arrives while a first substrate is still at the head,this merely causes further raising of the head, if necessary. Incontrast, with prior art systems using powered pistons, the resulttended to be the bursting of one or more packages. Furthermore, since atest head can be urged by gravity, the mechanism can be very simple. Itis also very consistent and reliable, whereas pneumatic systems inparticular are prone to variability. They also inevitably introducevibration.

Preferably the apparatus has two test stations, each having a test headadapted to be raised by a substrate moving along the conveying path.Preferably each test station includes means for deriving a signalrelated to the displacement of the test head. The apparatus may alsoinclude computing means which receives data from the displacementdetectors.

When a substrate reaches a test station, the test head is raisedthereby. If the substrate is "leaky", the test head will then fallsomewhat. Preferably the first test station is adapted to produce anadditive output signal, or the data are treated additively by thecomputer. That is, if a substrate causes the head to rise by x and thento descend by y, the resulting datum corresponds to (x+y). Preferablythe second test station leads to a differential datum corresponding to(x-y).

In conventional apparatus having two or more test stations, it isnecessary to make careful mechanical adjustments to the relative heightsof the test heads. In the present invention, particularly withgravity-urged heads, this is much less of a problem. Furthermore,adjustment can be made electronically, rather than mechanically. Thus ifa "good" (non-leaky) substrate is passed through the system, it shouldgive identical values at all test stations. If it does not, a correctioncan be applied by the computer to the data from one or more teststations.

Should it be desired to vary the load applied by a test head, this canbe done simply by adding or removing weights to it.

In further aspect the invention provides a method of testing asubstrate, comprising conveying the substrate through a test stationhaving a test head arranged so that passage of the substrate urgesdisplacement of the test head, which is urged against the substrate. Thedisplacement of the head is monitored to gain information about thesubstrate. Preferably there are two test stations, to which thesubstrate passes successively. Preferably the method uses apparatus asreferred to above.

An embodiment of the invention will now be described in more detail withreference to the accompanying drawing, in which the sole FIGURE is aschematic representation of apparatus embodying the invention.

The apparatus shows a conveyor belt 10 having an upper conveying run 12.The run 12 passes through two test stations 14, 16. These areessentially identical. Each has a test head 18 associated with avertical stem 20 which displaceably engages an encoder 22 which providesan output indicative of relative displacement of the stem 20. Theoutputs from the encoders 22 are passed to a computer 24.

Each head 18 is primarily a carrier for a length of roller chain 26.This is a row of free-running rollers 28. Each roller 28 extendstransversely of the conveyor run 12. It actually consists of amultiplicity of coaxial, independently rotatable rollers. Such rollerchain is available from, for example, Rexnord. (Its conventional use isfor conveyor belts, to provide a surface on which a conveyed article canbe held stationary while the belt continues to run.) At the upstream endof each head 18, there is a lead-in formation 30, the chain 26 extendingupwardly at an angle.

The heads are freely displaceable upwardly and downwardly. They arenormally gravitationally urged to contact the conveying run 12.(Alternatively they can have stop means so that they do not descendquite that far.) The force can be varied by adding or removing weights39 to a carrier 42. When a substrate 7, such as a packet of crisps,passes along the conveyor 10, it contacts the first lead-in 30 of thefirst head 18, causing it to rise. The amount of the rise is sensed bythe encoder 22. As the substrate passes between the head and theconveyor, for the main, flat length 32 of the head, the head should notmove. But if the packet leaks, the head will descend somewhat. Any suchdescent is also sensed by the encoder 22. The package leaves the firsttest station, and a similar sequence of events happens at the secondtest station 16.

The computer 24 receives the data from the two encoders 22. The data areanalysed to provide information relation to the nature of the package,particularly its compressibility and leakiness.

As a substrate passes through a test station, it provides two pieces ofdata; a "rise" value for the amount that the head is raised by thearrival of a substrate; and a "fall" value (which may be zero) relatingto the amount that the head falls while the substrate is beneath it.Preferably these pieces of data from the first station 14 are combinedadditively, whereas they are combined substractively at the secondstation 16. This can give extremely high sensitivity, as will beexplained.

With a conventional apparatus, having two test stations each having aplunger which is forced down onto a substrate, a sound package arrivingat the first station may allow the first head to move down by a distancesuch that the encoder counts a value of 150. The same will happen at thesecond test station. But consider a leaky package. At the first teststation, some air or gas will be squeezed out, e.g. so that the headmoves down by 200 counts. At the second station, if a similar amount offurther leakage occurs, the head will move down by 250 counts. Thus thefact that the package is leaky will be shown by the fact that the ratioof the counts from the first station to the counts from the secondstation is 200:250 instead of 1:1. With the apparatus embodying thepresent invention, in a similar situation, a package arriving at thefirst station may raise the first head by 150 counts. If the package issound, the same would happen at the second station. But if, once again,the package is leaky such that each head descends by 50 counts duringpassage of the package, then the first head is initially raised to aheight of 150 counts and then falls by 50 counts, giving a total(additive) value of 200. The compressed package is such that it willonly raise the second head through 100 counts. Assuming once again aleakage fall of 50 counts, the subtractive total is 50 counts. That isto say, the resulting values from the first and second heads are 200counts and 50 counts. Thus instead of a given degree of leakiness beingindicated by the ratio 200:250, it is indicated by the ratio 200:50.Clearly this is very much easier to detect. This means that much smallerleaks can be detected. This is further assisted by the consistency andlack of vibration resulting from the use of the gravity-urged system.

Data can also be passed to the computer 24 from a keyboard/display unit50. For example this may be used to set acceptable limits for substratethickness and leakiness. The apparatus may include means for removingrejected substrates from the conveyor 10., e.g. a blower 52 actuable bythe computer. The computer may also receive an input from a substratedetector 60 immediately upstream of the first test station 14.

The keyboard can also be used to calibrate the system and allow fordifferences between the test stations. Thus it is set to calibrationmode by means of the keyboard, and a standard, non-leaky substrate isrun through the system. If the rise values of the two heads 18 are notidentical, the computer stores a compensation value to be added to orsubstracted from the data given by one encoder.

I claim:
 1. Test apparatus comprising conveyor means for conveying anobject along a conveying path and through one or more test stationsarranged along the conveying path, at least one of said test stationscomprising a test head which is freely movable toward and away from theconveying path; said test head being urged solely by gravity towards theconveying path so that an object being conveyed along the path whichcontacts the head urges the head away from the conveying path; said testhead having a contact surface comprising an array of free runningrollers adapted to contact and to allow continuing movement of an objectalong the conveying path; said test station being actuated by thedisplacement of the test head by contact of the test head with an objectmoving along the conveying path, there being no additional means forsynchronising the action of the test station with the arrival of anobject at the test station; and means for monitoring displacement of thehead, said displacement monitoring means comprising means for measuringthe displacement of the head and means for providing an output signalrelated to the measured displacement of the head.
 2. Apparatus accordingto claim 1 wherein the apparatus comprises two of said test stations. 3.Apparatus according to claim 2 wherein said displacement monitoringmeans comprises means for measuring the displacement of the test head ofeach of the two test stations, and means for providing an output signalrelated to the displacement of each of the test heads of each of the twotest stations, and wherein the test apparatus includes computing meanswhich receives said output signals.
 4. Apparatus according to claim 2wherein said displacement measuring means comprises means fordetermining at each test station a rise value R related to the distancethrough which a respective test head is moved away from the conveyingpath by an object, and a fall value F related to the distance throughwhich the head returns towards the conveying path while in contact withan object; and means for determining (R+F) for a first of said two teststations and (R-F) for a second of said two test stations.
 5. Apparatusaccording to claim 1 wherein said test head comprises means for holdinga weight to establish a load applied by that test head.
 6. A method oftesting a sealed flexible package comprising conveying the package alonga conveyor path through a test station of a test apparatus, saidapparatus comprising conveyor means for conveying an object along aconveying path and through one or more test stations arranged along theconveyor path; at least one of said test stations comprising a test headwhich is freely movable toward and away from the conveying path; saidtest head being urged solely by gravity towards the conveying path sothat a package being conveyed alone the path which contacts the headurges the head away from the conveying path; said test head having acontact surface comprising an array of free running rollers adapted tocontact and to allow continuing movement of a package along theconveying path; said test station being actuated by the displacement ofthe test head by said contact of the test head with a package movingalong said conveyor path, there being no additional means forsynchronising the action of the test station with the arrival of apackage at the test station; and means for monitoring displacement ofthe head, said displacement monitoring means comprising means formeasuring the displacement of the head and means for providing an outputsignal related to the measured displacement of the head whereby passageof the package along conveyor path through said test station causesdisplacement of said test head, the method further comprising monitoringthe displacement of the test head to gain information about the package.7. A method according to claim 6 wherein said apparatus comprises two ofsaid test stations and wherein the method comprises passing the packagesthrough said two test stations.